Implements a new API to set a function entry hook for profiling.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 18c5ba6807b5d2d7ec9676206a5b6285ea321c7b..34995d09f78723c933a4e9f6760473b31e1eaf45 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -2915,16 +2915,34 @@ typedef bool (*EntropySource)(unsigned char* buffer, size_t length);
  * resolving the location of a return address on the stack. Profilers that
  * change the return address on the stack can use this to resolve the stack
  * location to whereever the profiler stashed the original return address.
- * When invoked, return_addr_location will point to a location on stack where
- * a machine return address resides, this function should return either the
- * same pointer, or a pointer to the profiler's copy of the original return
- * address.
+ *
+ * \param return_addr_location points to a location on stack where a machine
+ *    return address resides.
+ * \returns either return_addr_location, or else a pointer to the profiler's
+ *    copy of the original return address.
+ *
+ * \note the resolver function must not cause garbage collection.
  */
 typedef uintptr_t (*ReturnAddressLocationResolver)(
     uintptr_t return_addr_location);
 
 
 /**
+ * FunctionEntryHook is the type of the profile entry hook called at entry to
+ * any generated function when function-level profiling is enabled.
+ *
+ * \param function the address of the function that's being entered.
+ * \param return_addr_location points to a location on stack where the machine
+ *    return address resides. This can be used to identify the caller of
+ *    \p function, and/or modified to divert execution when \p function exits.
+ *
+ * \note the entry hook must not cause garbage collection.
+ */
+typedef void (*FunctionEntryHook)(uintptr_t function,
+                                  uintptr_t return_addr_location);
+
+
+/**
  * Interface for iterating though all external resources in the heap.
  */
 class V8EXPORT ExternalResourceVisitor {  // NOLINT
@@ -3185,6 +3203,20 @@ class V8EXPORT V8 {
       ReturnAddressLocationResolver return_address_resolver);
 
   /**
+   * Allows the host application to provide the address of a function that's
+   * invoked on entry to every V8-generated function.
+   * Note that \p entry_hook is invoked at the very start of each
+   * generated function.
+   *
+   * \param entry_hook a function that will be invoked on entry to every
+   *   V8-generated function.
+   * \returns true on success on supported platforms, false on failure.
+   * \note Setting a new entry hook function when one is already active will
+   *   fail.
+   */
+  static bool SetFunctionEntryHook(FunctionEntryHook entry_hook);
+
+  /**
    * Adjusts the amount of registered external memory.  Used to give
    * V8 an indication of the amount of externally allocated memory
    * that is kept alive by JavaScript objects.  V8 uses this to decide